Among the known linear-tracking pick-up arm drive assemblies of audio or video disc players is an assembly using a linear motor constructed by the combination of a stationary armature and a movable field magnet unit arranged to be longitudinally movable with respect to the stationary amature by the interaction between the constant magnetic field established by the field magnet unit and a variable control field induced by the current supplied to the coil forming part of the stationary armature. The pick-up arm of the audio or video disc player using such a linear motor is supported by the field magnet unit thus arranged and is moved over the surface of a recording disc set in the disc player as the movable field magnet unit is driven to move with respect to the stationary armature.
Another type of known linear-tracking pick-up arm drive assembly of an audio or video disc player uses a rotary motor for driving the pick-up arm by means of a suitable mechanical linkage connected to a movable unit on which the pick-up arm is supported.
In each of these known linear-tracking pick-up arm drive assemblied, the direction and the velocity of the movement of the pick-up arm can be varied by changing the polarity and the intencity of the current to be supplied to the coil forming part of the stationary armature of the linear motor or the coil included in the rotary motor. Difficulties are, however, encountered in enabling the pick-up arm to travel at a constant velocity during playing operation of the disc player and in causing the pick-up arm to stop accurately in a desired or specified position during or at the end of the playing operation.
An object of the present invention is, therefore, to provide an improved linear-tracking pick-up arm assembly which is capable of driving the pick-up arm of an audio or video disc player to move at a constant velocity during operation of the disc player and causing the pick-up arm to stop accurately in a desired or specified position during or at the end of the operation of the disc player.